1. Field of the Invention
The present invention relates to an image display device.
2. Description of the Related Art
In recent years, an image display device using light emitting elements such as organic electroluminescence elements (hereinafter, referred to as organic EL elements) has been developed actively. The light emitting elements are formed on, for example, a glass substrate together with pixel circuits for driving the light emitting elements.
FIG. 7 illustrates a circuit structure of an organic EL display according to a conventional technology. An organic EL element 101 is provided in each of pixel circuits PX. A cathode of the organic EL element 101 is grounded. An anode of the organic EL element 101 is connected to a power supply line Vcc through a driver thin film transistor (hereinafter, also referred to as TFT) 102. A storage capacitor 103 is connected between a gate and source of the driver TFT 102. The gate of the driver TFT 102 is connected to a signal line DL through a pixel switch 104. The signal line DL is connected to a signal input circuit XDV. The anode of the organic EL element 101 is grounded through a reset switch 105. The reset switch 105 is controlled by a reset switch control circuit RDV through a reset switch control line RL. The pixel switch 104 is controlled by a pixel switch control circuit YDV through a pixel switch scanning line GL. Each of the pixel circuits corresponds to a pixel.
FIG. 8 is a waveform diagram illustrating potential waveforms on the pixel switch scanning line GL and the signal line DL which are used for the pixel circuit PX of the conventional organic EL display. In the pixel circuit PX into which an image signal input from the signal line is to be written, firstly, the reset switch 105 is turned on through the reset switch control line RL. At this time, both the cathode and anode of the organic EL element 101 are reset to a ground potential, and simultaneously one end of the storage capacitor 103 is set to the ground potential. Next, the pixel switch 104 of the corresponding pixel is turned on through the pixel switch scanning line GL of the corresponding pixel. At this time, a signal voltage which is being applied to the signal line DL is applied to the other end of the storage capacitor 103, and hence the signal voltage is produced between both the ends of the storage capacitor 103. Next, when the pixel switch scanning line GL and the reset switch control line RL which are used for the corresponding pixel are turned off in the stated order, the signal voltage is held between both the ends of the storage capacitor 103. The voltage between both the ends of the storage capacitor 103 is equal to a gate-source voltage of the driver TFT 102, and hence the driver TFT 102 causes the organic EL element 101 to drive with a signal current corresponding to the signal voltage and to emit light. Therefore, according to the conventional organic EL display, even when a current flowing into the organic EL display element 101 makes the voltage applied between both the ends of the storage capacitor 103 unstable, the amount of current flowing into the organic EL element 101 is prevented from accidentally varying and an image including a plurality of pixels is displayed.
The image display device as described above is described in, for example, JP 2004-347993 A.
As illustrated in FIG. 7, the image display device described above requires two control lines per each pixel row. Therefore, a wiring structure for controlling the pixel circuits is complicated. When the reset switch control circuit RDV and the pixel switch control circuit YDV are externally mounted, the necessary number of connection terminals is two times the number of pixel rows.